Olefin metathesis is a catalytic process including, as a key step, a reaction between a first olefin and a first transition metal alkylidene complex, thus producing an unstable intermediate metallacyclobutane ring which then undergoes transformation into a second olefin and a second transition metal alkylidene complex according to equation (1) hereunder. Reactions of this kind are reversible and in competition with one another, so the overall result heavily depends on their respective rates and, when formation of volatile or insoluble products occur, displacement of equilibrium.

Metathesis reactions are extensively applied in the field of chemical reactions, e.g. Ring closing metathesis (RCM), Cross metathesis (CM), Ring opening metathesis (ROM), Ring opening metathesis polymerization (ROMP), acyclic diene metathesis (ADMET), self-metathesis, conversion of olefins with alkynes (enyne metathesis), polymerization of alkynes, and so on.

Typical applications of olefin metathesis but not limited are Reaction Injection Molding (RIM) of dicyclopentadiene (DCPD), which is an example of the ring opening metathesis polymerization; ROMP of norbornene derivates; ethenolysis, a chemical process in which internal olefins are degraded using ethylene as the reagent. The reaction is an example of cross metathesis; CM of ethene with 2-butene; depolymerization of unsaturated polymers.
Of potentially greater interest than homo-coupling (equation 3a) is cross-coupling between two different terminal olefins (equation 3b). Coupling reactions involving dienes lead to linear and cyclic dimers, oligomers, and, ultimately, linear or cyclic polymers (equation 6). In general, the latter reaction is favoured in highly concentrated solutions or in bulk, while cyclisation is favoured at low concentrations. When intra-molecular coupling of a diene occurs so as to produce a cyclic alkene, the process is called ring-closing metathesis (equation 2). Cyclic olefins can be opened and oligomerised or polymerised (ring opening metathesis polymerisation shown in equation 5). When the alkylidene catalyst reacts more rapidly with the cyclic olefin (e.g. a norbornene or a cyclobutene) than with a carbon-carbon double bond in the growing polymer chain, then a “living ring opening metathesis polymerisation” may result, i.e. there is little termination during or after the polymerization reaction. Strained rings may be opened using an alkylidene catalyst with a second alkene following the mechanisms of the Cross Metathesis. The driving force is the relief of ring strain. As the products contain terminal vinyl groups, further reactions of the Cross Metathesis variety may occur. Therefore, the reaction conditions (time, concentrations, . . . ) must be optimized to favor the desired product (equation 4). The enyne metathesis is a metalcarbene-catalyzed bond reorganization reaction between alkynes and alkenes to produce 1,3-dienes. The intermolecular process is called Cross-Enyne Metathesis (7), whereas intramolecular reactions are referred as Ring-Closing Enyne Metathesis (RCEYM).
The cross-metathesis of two reactant olefins, where each reactant olefin comprises at least one unsaturation site, to produce new olefins, which are different from the reactant olefins, is of significant commercial importance. One or more catalytic metals, usually one or more transition metals, usually catalyze the cross-metathesis reaction.
One such commercially significant application is the cross-metathesis of ethylene and internal olefins to produce alpha-olefins, which is generally referred to as ethenolysis. More specific, the cross-metathesis of ethylene and an internal olefin to produce linear α-olefins is of particular commercial importance. Linear α-olefins are useful as monomers or co-monomers in certain (co)polymers poly α-olefins and/or as intermediates in the production of epoxides, amines, oxo alcohols, synthetic lubricants, synthetic fatty acids and alkylated aromatics. Olefins Conversion Technology™, based upon the Phillips Triolefin Process, is an example of an ethenolysis reaction converting ethylene and 2-butene into propylene. These processes apply heterogeneous catalysts based on tungsten and rheniumoxides, which have not proven effective for internal olefins containing functional groups such as cis-methyl oleate, a fatty acid methyl ester.
1-Decene is a co-product typically produced in the cross-metathesis of ethylene and methyl oleate. Alkyl oleates are fatty acid esters that can be major components in biodiesel produced by the transesterification of alcohol and vegetable oils. Vegetable oils containing at least one site of unsaturation include canola, soybean, palm, peanut, mustard, sunflower, tung, tall, perilla, grapeseed, rapeseed, linseed, safflower, pumpkin, corn and many other oils extracted from plant seeds. Alkyl erucates similarly are fatty acid esters that can be major components in biodiesel. Useful biodiesel compositions are those, which typically have high concentrations of oleate and erucate esters. These fatty acid esters preferably have one site of unsaturation such that cross-metathesis with ethylene yields 1-decene as a co-product.
Vegetables oils used in food preparation (fritting of meat, vegetables, . . . ) can be recuperated and after purification, be converted applying e.g. ethenolysis into useful products applicable in biodiesel.
Biodiesel is a fuel prepared from renewable sources, such as plant oils or animal fats. To produce biodiesel, triacylglycerides, the major compound in plant oils and animal fats, are converted to fatty acid alkyl esters (i.e., biodiesel) and glycerol via reaction with an alcohol in the presence of a base, acid, or enzyme catalyst. Biodiesel fuel can be used in diesel engines, either alone or in a blend with petroleum-based diesel, or can be further modified to produce other chemical products.
Several Metal-carbene complexes are known for olefin metathesis however the difference between those structures can be found in the carbene part. Patents WO-A-96/04289 and WO-A-97/06185 are examples of metathesis catalysts having the general structure

Where:
M is Os or Ru, R and R1 organic parts from the carbene fragment which have a great structural variability, X and X1 are anionic ligands and L and L1 represents neutral electron donors. “anionic ligands” are, according the literature in the field of olefin metathesis catalysts, ligands which are negative charged and thus bearing a full electron shell when they are removed from the metal center
A well-known example of this class of compounds is the Grubbs 1st generation catalysts

Another well-known example of this class of compounds is the Grubbs' 2nd generation catalyst which is described in WO-A-0071554 and the hexa-coordinated “Grubbs 3rd generation catalyst described in WO-A03/011455.

There are still some other well-known catalysts described in literature which are very useful in the area of olefin metathesis, and which serve as background information for this application. These catalysts are described in US 2002/0107138 A1 and WO-A-2004/035596 and are respectively known as the “Hoveyda catalysts” and the “Grela catalyst”

Furthermore, other catalysts are known where both carbon atoms of the carbene fragment are bridged, a few of these representatives are given

The bridged carbene fragment was firstly synthesized by Hill et al. (K. J. Harlow, A. F. Hill, J. D. E. T. Wilton-Ety, J. Chem. Soc. Dalton Trans. 1999, 285-291), however the structure was wrongly interpreted. Furstner et al. corrected this misinterpretation (J. Org. Chem. 1999, 64, 8275-8280) and a full characterization was described. It followed that reorganization takes place whereby the carbon atoms of the carbene fragment are bridged and generating in this specific case a “3-phenyl-indenylidene carbene” (Chem. Eur. J. 2001, 7, No 22, 4811-4820). Analogues of this catalyst bearing one NHC-ligand and one phosphine ligand where described by Nolan in WO-A-00/15339. These types of compounds are not only catalysts for the olefin metathesis; they also can be used as starting product to produce other ruthenium-carbene compounds via cross metathesis (WO-A-2004/112951).
Furthermore, in US-A-2003/0100776 on page 8, paragraph [0087] are catalysts described where the carbon atoms of the carbene part are bridged and whereby the newly formed cyclic group can be aliphatic or aromatic and can bear substituents or hetero atoms. Additionally, it is said that the generated ring structure is constructed of 4 to 12 and preferable 5 to 8 atoms contains. However, no explicit ring structures or examples are described or given.
In PCT/US2010/059703 (WO 2011/100022 A2) an indenylidene based catalyst is described whereby one phosphine ligand is substituted by an neutral donor ligand which is linked to the indenylidene carbene. The resulting catalyst is a 3-phenylindenylidene Hoveyda analogue catalyst.
In PCT/US2011/029690 (WO 2011/119778 A2) a hexa-coordinated catalyst is claimed, however in this document no catalysts were isolated, a synthetic method for the in-situ generation of olefin metathesis catalysts is disclosed since according to Schrödi the synthesis of these complexes is relatively cumbersome. The synthesis usually involves more than one step and requires isolation of the catalysts to remove catalyst-inhibiting byproducts such as liberated phosphines. The resulting in-situ generated catalysts are all phenylindenylidene Hoveyda analogue catalysts.
Other catalysts where the carbon atoms of the carbene part are bridged having the indenylidene basic structure are until now not know

Despite the advances achieved in the preparation and development of olefin metathesis catalysts, a continuing need exists for new improved synthetic methods and new catalysts. Of particular interest are methods that provide the preparation of new catalysts, which easily can be prepared on industrial scale.
Furthermore, the instant invention's metathesis catalyst compounds provide both a mild and commercially economical and an “atom-economical” route to desirable olefins, which in turn may be useful in the preparation of linear alpha-olefins, unsaturated polymers, cyclic olefins, etc.
The synthesis of RuCl2(PCy3)2(3-phenylindenylene) has proven useful in providing an easy route to ruthenium alkylidenes which avoids costly diazo preparations (Platinum Metals Rev. 2005, 49, 33).
In order to obtain an economically viable process for linear α-olefins (e.g. 1-decene) production via the cross-metathesis of ethylene and biodiesel (such as animal or vegetable oils), higher activity catalysts or more stable catalysts must be developed. Moreover, there is still a need for the development of catalysts with equivalent or better performance characteristics but synthesized directly from less expensive and readily available starting materials.